For a period of about six days centered on July 19, 1994, fragments of Comet Shoemaker-Levy 9 are expected to collide with Jupiter, the solar system's largest planet. No such event has ever before been available for study. The energy released by the larger fragments during impact will be more than 10,000 times the energy released by a 100-megaton hydrogen bomb! Unfortunately for observers, the collisions will occur on the night side of Jupiter, which also will be the back side as seen from Earth. The collisions can still be studied in many ways, nevertheless, by spacecraft more advantageously located, by light of the collisions reflected from Jupiter's satellites, and by the effects of the impacts upon the Jovian atmosphere. (The impact sites will rotate into view from Earth about 20 minutes after each collision.)
Stupendous as these collisions will be, they will occur on the far side of a body half a billion miles from Earth. There will be no display visible to the general public, not even a display as obvious as a faint terrestrial meteor. Amateur astronomers may note a few seconds of brightening of the inner satellites of Jupiter during the impacts, and they might observe minor changes in the Jovian cloud structure during the days following the impacts. The real value of this most unusual event will come from scientific studies of the comet's composition, of the impact phenomena themselves, and of the response of a planetary atmosphere and magnetosphere to such a series of "insults".
This booklet offers some background material on Jupiter, comets, what has and possibly will happen, and how scientists propose to take advantage of the impact events.